Stern drive marine propulsion systems have generally been constructed to transfer power from a power supply to an output mechanism in order to move and direct a marine vessel through the water. The output mechanism, which may be considered as part of or separate from the stern drive, is typically a propeller and the power supply is typically an engine, motor, or some other similar source of power.
Conventional stern drive systems include an input shaft, an output shaft, gears and/or sprockets, and a clutch. They have been used in an inboard/outboard drive arrangement wherein the engine, or power supply, is located in the boat and the stern drive is located wholly or substantially outside the boat. Stern drive is interchangeably referred to in the art as an inboard/outboard or I/O.
In one example of a conventional stern drive system, the input shaft drives an intermediate shaft via a gearing arrangement which in turn drives the output shaft via an additional gear mechanism. The reversing mechanism is integrated into the gearing arrangement by using two gears which can be coupled to the intermediate shaft and which couple a gear on the input shaft. Accurate positioning and tolerances of the various elements of such a conventional stern drive is necessary in order to assure proper alignment and interconnection of the respective gears and shafts. In addition, such conventional stern drives require an appropriately sized underwater body which may result in lower hydrodynamic efficiency. Moreover, due to the precise positioning and resulting specific tolerances of the gears and shafts, the parts of such a conventional stern drive are relatively expensive to manufacture.
One alternative stern drive marine propulsion system employs a plurality of chains, sprockets, and/or gears to transfer power from the power input shaft to the output shaft. The chains, sprockets, and shafts of such a system, however, are ordinarily positioned in an oil-filled chamber, which is necessary to provide lubrication for the individual components. Moreover, such systems have presented maintenance problems due to serviceability and wear of the parts involved.
In addition, a variety of endless belt-driven stern drives have been proposed but have not yet been competitive with other types of stern drives. One possible reason for the lack of success is that the conventional construction seems to preclude clean hydrodynamic lines. Thus, the known designs generally produce excessive drag in the water. Another disadvantage is that the belt-driven systems usually require a separate transmission located within the boat to determine the rotational direction of the propeller and to minimize the size and complexity of the stern drive. A separate transmission, however, increases the overall complexity and cost of the complete marine propulsion system.
With regard to the hydrodynamic lines of a belt driven stern drive, it has been proposed to reduce the cross section of the lower part of the housing by bending the endless belt as it rotates between the input and propeller shafts by use of stationary skid plates mounted in the housing. Such systems, however, require the presence of lubricant in the belt housing in order to reduce the friction/heat between the belt and the skid plates as well as heat generated elsewhere in the drive. Such a lubrication system again adds to the complexity and cost of the overall design. Moreover, that proposed design does not address the problems associated with the required separate transmission.
A further problem with many belt-driven systems has been the complex mechanisms required to provide additional pretensioning and dynamic tensioning to the belt drive. Such mechanisms have added unnecessary costs and complexity to the stern drive.
The present invention provides a reversible stern drive system which substantially obviates one or more of the limitations and disadvantages of the described prior stern drive systems. Embodiments of the invention reduce the need for the tight tolerances and maintenance expense associated with numerous gears. Additional advantages include improved hydrodynamic lines without requiring a separate belt housing lubricant system; and a simple mechanism to provide the necessary tension to the belt to transmit power from the engine to the propeller. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned in practice of the invention.